Composites Flashcards
What is a Composite?
A solid with 2 or more distinct constituent materials or phases(enamel, bone, dentin and reinforced polymers all qualify)
Composite is normally referred to as:
reinforced polymer system used for restoring hard tissues
What are the 4 components of a composite?
- organic polymer matrix
- Inorganic filler particles
- Coupling agent
- Initiator-accelerator system
What usually makes up the organic polymer matrix?
Bis-GMA, UDMA or Silorane-new low-shrinkage monomer
4 types of inorganic filler particles
- quartz or glass
- sol-gel derived ceramics
- microfine silica
- nanoparticles
What is the biggest component of a composite by weight
Inorganic filler particles
What do inorganic filler particles provide for composite
- translucency
2. reduces shrinkage 3.reinforces resin matrix
What does a coupling agent do?
forms a bond between inorganic filler particles and organic resin matrix. Also makes hydrophobic and enhances mechanical properies
-silane is most common
What does the initiator-accelerator system do?
polymerize and cross-links system into a hardened mass Ex:camphorquinone absorbs blue light
Purpose of composites
esthetics, high stress areas. (they have lower wear and lower expansion than acrylics and silica)
Composites are classified by:
- Shape
- particle size
- Particle distribution of the filler
Are nano hybrids a true nanofill?
no because they are mixed with bigger chunks
Nanofills particle size
1-100 nm
Camphorquinone
absorbs blue light and starts curing process
is an initiator-accelerator
how are composites polymerized
free radical addition polymerization of methacrylate monomers
Stages of polymerization
- intiation
- Propagation
- Termination
What factors influence degree of polymerization?
vanderwalls space(molecular bond length) and free space(due to random thermal energy and rotational mvmt)
Methods to decrease contraction during polymerization
- add more inorganic filler
- add more prepolymerized particles
- use methylacrylate particles with HIGH molecular wieght
Activation and polymerization methods inculde
- light activation via blue light (465nm)
- chemical activation
- dual curing (chem and light)
how long does setting reaction continue?
24 hours
when is mechanical strength attained after placing composite?
immediately after curing the restoration
how long does it take composite to loose capability to flow when exposed to light?
60-90 seconds
Setting times for chemically activated composites range from
3-5min
What do inorganic oxides provide to a composite?
coloration
What properties can be improved if composites are judiciously developed?
- modulus
- strength
- fracture toughness
- wear resistance
- thermal expansion
- chemical corrosion resistance
what size particles are mixed in micro hybrids?
.04-1 micrometers
Microhybrid qualities
good stress and wear resistance but get dull with time
what is cermet?
glasses fused with metals such as gold, silver and titanium
what is the purpose of cermet?
to improve the strength of glass ionomers
what are the properties of macrfills?
- early composites
- spherical or irregular shaped particles
- opaque
- low resistance to wear
What is a hybrid composite?
two types of fillers blended together, has irregular shapes
-fine particles 2-4 micrometers
and 5-15%microfine particles(usually silica)
what makes up microhybrid composites?
77-84%filler by weight
- fine particles size .04-.1 micrometer blended with microfine silica
- has irregular shapes
what does distribution of filler particles provide
efficient packing so high filler loading is possible
Hybrids and microhybrids pros and cons
good clinical wear resistance, mechanical properties for stress-bearing spots
Lose surface polish, becoming rough and dull
purpose of fillers:
- reinforce resin matrix
- provide appropriate translucency
- control volume shrinkage of the composite during polymerization
Most common monomers used are:
aromatic dimethacrylates
(also bisGMA and UDMA)
-high viscosity so dilutants must be added
coupling agent
silane applied to inorganic particles to surface treat the fillers before being mixed with the unreacted monomers
which composite type has the best polish and esthetics?
Microfilled(but has higher shrinkage)
Which composite has the highest volume of inorganic filler?
Nanocomposite 78.5%
Which composite has the lowest volume of inorganic filler?
Flowable-syringeable and lower modulus
disadvantage: has higher wear
Advantages of nanocomposite
high polish, high strength , high modulus
disadvantage of microfilmed composite
higher shrinkage
disadvantage of flowable composite
higher wear
advantages of multipurpose composite
high strength high modulus
are Glass ionomers classified as composites?
yes
Glass ionomer properties include
water based material
acid-base setting reaction
high elastic modulus
more stiff
low elastic modulus
less stiff, higher fracture toughness
